Hand drill with safety switch actuated by end-play movement of shaft



Oct. 7, 1969 R. F. BERCHTOLD 3,471,662

HAND DRILL WITH SAFETY SWITCH ACTUATED BY END'PLAY MOVEMENT OF SHAFT Filed Feb. 27, 1967 INVENTOR.

Ross/er [EsRCHTN-D BY CM 1M United States Patent 7 Claims ABSTRACT OF THE DISCLOSURE Certain hand tools, such as hand drills for drilling metal such as the commonly known hand electric drill for drilling sheet metal; for example in aircraft work, the operator must start to drill by closing a switch in the electrical circuit connected to the drill motor, and the drill will run continuously even after the drill passes through the sheet metal. Likewise, in a drill press where the drill is brought down into engagement with the work, the drill must be started by closing a switch and it will run even when the operator lifts the drill from the work. This results in a rather dangerous situation when the work catches to the drill and is rotated by it.

Applicant has discovered that by providing a small amount of end play between the quill shaft of the drill and the drill itself and spring loading the shaft to move outward that the quill will move axially toward the drill when the drill bit engages work and this end play motion can be used to close a switch to start and stop the drill motor.

The same feature can be adapted to sanders, grinders, and other cutting tools Where the tool bit is moved into engagement with the work by some means other than the motor that rotates the tool, cutting bit or cutting member.

This invention relates to tools and, more particularly, to tools that move a cutting bit which engages work.

It is, accordingly, an object of the invention to provide an improved electric drill.

Another object of the invention is to provide an improved electric drill having an automatic starting device.

Another object of the invention is to provide an improved starting device in combination with a tool.

With the above and other objects in view, the present invention consists of the combination and arrangement of parts hereinafter more fully described, illustrated in the accompanying drawing and more particularly pointed out in the appended claims, it being understood that changes may be made in the form, size, proportions, and minor details of construction without departing from the spirit or sacrificing any of the advantages of the invention.

In the drawing:

The figure is a longitudinal cross sectional view of an electric drill according to the invention.

Now with more particular reference to the drawing, the view shown indicates a conventional type of electric drill which may be held in the hand of a person or may be supported on a press fixture of a type that is well known to those skilled in the art. This type of drill is used by mechanics, electricians, and other workmen almost universally. These electric drills are usually provided with a supporting stand with a handle so that they can be used as a post drill. The same drill is often provided with accessories for grinding, bufiing, polishing, sawing, and other functions. The attachments that are ordinarily used with 3,471,662 Patented Oct. 7, 1969 this type of drill are not shown on the drawing since they are so well known in the art so as to be obvious.

The drill shown has a casing 10 that may be made of some die casting or the like and the casing is provided with a motor housing 12 separated by a supporting structure 11 which carries part of the bearings and which may be connected together in a suitable manner. The electric motor may be connected to the quill shaft 16 in the well known manner by means of gears 17 which are reduction gears and which are provided in the conventional manner. A thrust bearing 22 is provided on the quill shaft to absorb the thrust of the quill shaft when the drill bit 38 engages work.

The quill shaft 16 is supported in bearings 24 and 15. Bearing 15 is supported in a bore as shown in the boss attached to the housing 13.

A thrust washer 18 is supported on the shaft 16 and the compression spring 19 is a helical spring supported on the shaft 14 and compressed between nut 20 with threadably supported on the shaft 14, thus, the quill shaft and drill bit are urged away from the switch element 29.

The usual chuck 37 is supported on the shaft 14 and it may hold a drill'bit 38 or some other tool or accessory as mentioned above.

The switch elements 29 and 30 are supported on the screw 32 that threadably engages the partition 23 and the switch elements 29 and 30 are supported between the head 31 of the screw and the insulated washers 32 and 3-4. The switch has contacts 27 and 28 and normally the switch is in the open position as shown. When drill bit 38 engages work it will compress the spring 19 and urge quill shaft toward the switch so that the terminal end 26 of the end 25 of the drill engages the switch element 29 to force the contact 27 into engagement with contact 28, thereby, connecting a source of power through wires 35 and 36 to the drill motor. It will be noted that as soon as the force is relieved on the drill bit 38 that the spring 19 will again move the quill shaft and open the contacts 27 and 28 thus stopping the motor. The nut 20 may be tightened to compress the spring 19 so that a greater force will be necessary on the drill bit 38 to operate the drill.

The foregoing specification sets forth the invention in its preferred practical forms but the structure shown is capable of modification within a range of equivalents without departing from the invention which is to be understood is broadly novel as is commensurate with the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. An electric tool comprising a motor having a shaft,

means on said motor adapted to be engaged by a supporting means,

connecting means on said tool connecting a tool bit adapted to exert a force on work to said motor,

a switch on said tool for connecting said motor to a source of electricity,

said connecting means being movable relative to said tool when said tool bit exerts a force on said work, means on said connecting means for engaging said switch for closing said switch when said connecting means moves relative to said tool whereby said source of electricity is connected to said motor,

said connecting means comprising a rotatable shaft supported on said motor,

said rotatable shaft being connected to said motor shaft,

said rotatable shaft has a limited amount of end play whereby said shaft may move axially relative to said riiotorwhen a force is' exerted on said tool bit,

said motor shaft and said rotatable shaft being spaced from each other and generally parallel to each other, and said means for engaging said switch being disposed on said shaft.

2. The tool recited in claim 1 wherein said rotatable shaft has an end engaging said switch to actuate said switch when said rotatable shaft moves axially.

3. The tool recited in claim 2 wherein said shaftis connected to said motor through reduction gears.

4, The tool recited ni claim 1 wherein resilient means is disposed onsaid shaft urging said shaft away from said switch.

5. The tool recited in claim-4 wherein said resilient means comprises a helical spring.

' '6. The tool recited in claim 5 wherein means is provided to adjust the compression force exerted by said spring.

H 7 The tool recited in claim 1 wherein said connecting 'means further comprises a chuck on said shaft References Cited ROBERT K. SCHAEFER, Primary Examiner 15 ROBERT A. VANDERHYE', :Assistant Examiner Us. C1. XQR. j 

